This invention relates to a display panel having conductive contact media disposed between upper and lower electrodes which function as the gap material between the electrodes and more particularly to a liquid crystal display panel having improved electrical contacts between the upper and lower electrodes, and improved display quality, speed and color.
Conventional liquid crystal display panels have a spacing, or gap, between upper and lower electrode bearing substrates. A common electrode, generally of a metal, is in electrical contact with the electrodes of each substrate. In general, a soft metal, e.g. indium, is utilized as the electrical connection between the upper and lower substrates. In order to provide this connection, the soft metal is placed into a gap created in one substrate and then the two substrates are forced into parallel, opposed alignment, spaced apart by the soft metal. One disadvantage of this structure and method is the tendency toward contact failure between the soft metal and the electrodes. To overcome this defect resinous adhesive agent including a conductive metal, e.g. silver, has been printed on either the upper or lower substrate prior to construction of the panel. This resinous agent is generally applied in the form of a paste. However, unacceptably high proportions of electrical contact failure between the upper and lower electrodes when using such pastes are known. These failures occur during the necessary steps undertaken in the process of manufacturing a liquid crystal panel. To manufacture a panel, a matrix of panel substrates is formed on a master substrate and then each panel substrate is separated by mechanical means. In a conventional construction, a conductive resinous adhesive silver paste is positioned on each individual substrate panel prior to the separation step. When the force necessary to separate each individual panel is applied, the silver paste in the adhesive material tends to disassociate itself therefrom. As a result, when the individual substrates are brought into opposition, contact failure sometimes occurs between the upper and lower substrates. The contact failure can be adhesive or electrical in nature. When the adhesive resin content of the silver paste is increased, it becomes difficult to maintain the silver particles in electrical contact with each other. This results in unacceptable levels of contact failure between the upper and lower electrodes. Conversely, if the concentration of the silver particles in the silver paste is increased to overcome this drawback, the adhesive properties of the paste are diminished, thereby also causing unacceptable rates of contact failure. Optimum ratios of resins and silver particles, even when mixed properly, do not exist, since variations in conditions such as humidity and temperature of manufacture, as well as drying temperature, all cause variations in the properties of the silver paste product. Furthermore, the average particle diameter of the silver particles in the silver paste varies. It is generally more than about seven microns, although particles smaller than this size do regularly appear. Additionally, the shape of the particles also varies. Thus, two particles can be generally of the same size, but differ enough in shape to effect the alignment of the opposed display panels. This variation in particle sizes and shapes causes great difficulty in aligning in parallel the opposed substrate plates.